The present invention relates generally to a clamping device which may be used in connection with a machine tool for clamping a workpiece or tool on a machine's table. More particularly, it relates to a slide wedge clamp which is provided with a clamp bolt to be fastened manually. The force applied for screwing it up is transmitted and magnified through a slide wedge mechanism which can powerfully clamp a workpiece.
A device which is similar to the clamp of the present invention is disclosed in FIG. 15 of U.S. Pat. No. 4,049,253 and is known as the toe clamp.
This toe clamp consists of a work-engaging member E disposed above a T-shaped groove 1 in the top 12 of a table B of a milling machine and a nut A disposed in the T-sectioned groove 1. When a clamping screw C is screwed into the nut A, the nut A is lifted after the advancing screw C comes into contact with a swivel head D and its shoulder is pressed against the mating shoulder of the T-shaped groove 1 so that the nut A is fixed relative to the table B. Shoulder bolt F is screwed into the threaded bore 8 of the nut A to drive forward the work-engaging member E as it is pressed down by the bolt 9. A workpiece H is clamped by the forward end 16 of the work-engaging member E which is in contact with side 17 of the workpiece.
This toe clamp, however, is known to have the following defects:
(a) Since the shoulder bolt F and the clamping screw C are set through the work-engaging member E in an inclined orientation, it is rather difficult to fasten them. This is especially true in the case of a horizontal machine tool with its box-shaped work pallet because the workpiece H has to be clamped to a vertical side of the pallet and the clamping screw C has to be screwed diagonally upward. The workability is then particularly unfavourable.
Moreover, the bolt bore and threaded bores 8 and 18 have to be provided in the work-engaging member E and nut A inclined. This adds to their manufacturing costs.
(b) Since the workpiece H to be clamped is directly placed on the top of the table B, vertical drilling work on it is likely to result in injury of the table B by the drill tip. Therefore, this device is less suited for clamping of this kind of workpieces which are to be vertically drilled.
(c) Since the working mechanism is such that the work-engaging member E is driven forward as it is pressed down to clamp the workpiece H, the bottom of the work-engaging member E cannot be supported by the top of the table B, and the work-engaging member E has to be retained in a raised state. Hence, the portion of shoulder bolt F which runs through the compression spring G is subjected a high bending moment as well as a tensile load. This interferes with the powerful clamping action which is desired.